1. Field of the Invention
The present invention relates to an ultrasonic probe and an ultrasonic diagnostic apparatus with side lobes reduced by weighting a transmission intensity and a reception intensity of ultrasonic waves to be transmitted and received.
2. Description of the Related Art
An ultrasonic probe is a device for, with an object of visualization or the like of the inside of an object, irradiating ultrasonic waves to the object and receiving reflected waves from interfaces having different acoustic impedances in the object. As ultrasonic image apparatuses in which such an ultrasonic probe is adopted, there are a medical diagnostic apparatus and the like for inspecting the inside of a human body.
As the ultrasonic probe, there is one called a linear array ultrasonic probe. This linear array ultrasonic probe has a piezoelectric element unit carrying out transmission and reception of ultrasonic waves. The piezoelectric element unit includes plural piezoelectric elements that are arranged in parallel at fixed intervals in an array direction. On a human body side of the piezoelectric unit, an acoustic matching layer and an acoustic lens are stacked sequentially to cover all the piezoelectric elements. On a side opposite to the human body side of the piezoelectric unit, a back member is provided.
When the linear array ultrasonic probe is used, a drive circuit applies drive signals to the respective piezoelectric elements. At the same time, phases of the drive signals applied to the respective piezoelectric elements are shifted by a delay circuit, whereby irradiation positions of the ultrasonic waves are moved in the array direction to scan a patient.
The ultrasonic waves generated from the respective piezoelectric elements are transmitted to the human body via the acoustic matching layer and the acoustic lens. Then, the piezoelectric element unit receives reflected waves generated by mismatching of acoustic impedances in the human body, whereby an internal structure of the human body is visualized and shown on a display monitor.
When the piezoelectric element unit is manufactured, first, the acoustic matching layer is joined to a rectangular piezoelectric material block. Next, the back member is joined thereto and only the piezoelectric material block is subjected to dicing at predetermined intervals to change the piezoelectric material block into arrays, that is, divide the piezoelectric material block into plural piezoelectric elements.
Next, the acoustic lens is joined to the acoustic matching layer. Finally, the drive circuit and the respective piezoelectric elements are electrically connected, whereby the ultrasonic probe is completed.
Incidentally, in the linear array ultrasonic probe, when a drive signal of a rectangular waveform is applied to the respective piezoelectric elements, side lobes in sound fields in a lens direction cause problem or the sound fields in the lens direction are made non-uniform.
Therefore, in recent years, a technique for weighting intensities of ultrasonic waves transmitted from a piezoelectric element unit to reduce side lobes or to make sound fields uniform has been disclosed.
For example, an ultrasonic probe having respective piezoelectric elements divided in a lens direction at varied intervals to weight an area density of the piezoelectric elements with respect to the lens direction is disclosed (see, for example, JP-A-2003-9288).
In addition, an ultrasonic probe having respective piezoelectric elements divided at fixed intervals in a lens direction to weight drive signals applied to the divided respective piezoelectric elements is also disclosed (see, for example, JP-A-5-38335).
Moreover, an ultrasonic probe having an acoustic matching layer divided at varied intervals in a lens direction to weight an area density of the acoustic matching layer in the lens direction is also disclosed (see, for example, JP-A-11-146492).
However, the ultrasonic probes disclosed in JP-A-2003-9288, JP-A-5-28331, and JP-A-11-146492 have problems described below.
(JP-A-2003-9288)
When the piezoelectric element unit is manufactured, the respective piezoelectric elements are completely divided in the lens direction. Thus, contrivance for positioning pieces of the respective piezoelectric elements with respect to one another is required, which causes an increase of manufacturing steps and an increase in manufacturing cost.
In addition, when resin or the like is filled among the pieces of the respective piezoelectric elements, electrodes formed on end faces of the respective piezoelectric elements overlap the resin partially, adhesion of the electrodes to the piezoelectric elements falls to deteriorate reliability in the apparatus.
Moreover, even if grooves for weighting are formed in the respective piezoelectric elements, ultrasonic waves emitted from the piezoelectric elements cause acoustic crosstalk in the acoustic matching layer. Thus, it is difficult to obtain a desired sound pressure distribution.
(JP-A-5-38335)
Structures of the apparatus and the circuit are complicated to cause deterioration in reliability in the ultrasonic probe and an increase in cost for a manufacturing process.
(JP-A-11-146492)
Even if grooves for weighting are formed in the respective acoustic matching layer, ultrasonic waves emitted from the piezoelectric elements have already caused acoustic crosstalk in the piezoelectric elements. Thus, it is difficult to obtain a desired sound pressure distribution.